Regular big trianglemesh produces holes

[JNieswand]

Hi there!

I am using instant-meshes in my project and am quite satisfied with the results. However, I noticed problems with input meshes that consist of regular tiny triangles, e.g. like this:

This mesh has ca. 2e6 vertices, 4e6 triangles. I try to convert it to quite a coarse mesh, ca. 1000 vertices as target. The result always ends up having holes:

If i remesh my input triangle mesh with a third party software, I don't have any holes in the end result. Input mesh structure then looks something like:

The triangle mesh has ca. 5e5 vertices.
Any idea what could be the reason?